The present technology relates to a variable focal length lens system and an image pickup apparatus. More particularly, the present technology relates to a technical field of a variable focal length lens system which is suitable for a digital camera or a video camera and particularly in which the angle of view in a wide angle end state ranges approximately from 24 to 35 mm in a 35 mm equivalent angle of view and the zoom ratio is approximately four to seven times and an image pickup apparatus which includes such a variable focal length lens system as just described.
A method is known wherein an image pickup device which uses a photoelectric conversion element such as a CCD (Charge Coupled Device) element or a CMOS (Complementary Metal Oxide Semiconductor) element as recording unit for a camera is used such that an image of an image pickup object formed on a face of the image pickup element is converted into and recorded as an electric output.
Together with the progress of a microprocessing technique in recent years, enhancement of the operation speed of a central processing unit (CPU) and the integration of a storage medium has been achieved. Thus, it has become possible to carry out high speed processing of a large amount of image data which has been impossible to handle. Also with regard to a light receiving device, high integration and miniaturization have been achieved, and high integration has made it possible to record with a higher spatial frequency and the miniaturization has achieved miniaturization of the entire camera.
However, such high integration and miniaturization as described above have decreased the light receiving area of individual photoelectric conversion elements and decreased the electric output power. This has given rise to a problem that the influence of noise increases. In order to prevent the problem, the aperture ratio of the optical system has been increased to increase the amount of light which reaches the light receiving device.
Or, very small lens elements of a microlens array have been located immediately in front of individual photoelectric conversion elements. While this microlens array introduces a ray, which is directed to a portion between adjacent ones of light receiving elements, to the light receiving elements, it provides a restriction to the position of the exit pupil of the lens system. If the position of the exit pupil of the lens system approaches the light receiving elements, namely, if the angle of a main ray, which comes to a light receiving element, with respect to the optical axis becomes great, then an off-axis ray directed to a peripheral portion of the screen defines a great angle with respect to the optical axis. As a result, the ray fails to come to the light receiving element, resulting in shortage in light amount.
Generally, a variable focal length lens system wherein the angle of view in a wide angle end state, in which the focal length is shortest, ranges approximately from 24 mm to 35 mm in a 35 mm equivalent angle of view and the angle of view in a 35 mm equivalent angle of view in a telephoto end state, in which the focal length is longest, exceeds 50 mm, is called standard variable focal length lens system.
As this standard variable focal length lens system, a variable focal length lens system of a positive-negative-positive-positive four-lens-group configuration such as those disclosed in Japanese Patent Laid-Open Nos. 2002-323656, 2003-241092 and 2007-114432 has been used frequently. Also a variable focal length lens system of a positive-negative-positive-negative-positive five-lens-group configuration such as those disclosed in Japanese Patent Laid-Open Nos. 2009-156891 and 2010-237453 has been used frequently.
The variable focal length lens system of a positive-negative-positive-positive four-lens-group configuration includes a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power and a fourth lens group having a positive refracting power, disposed in order from the object side to the image side.
The variable focal length lens system of a positive-negative-positive-negative-positive five-lens-group configuration includes a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, a fourth lens group having a negative refracting power and a fifth lens group having a positive refracting power, disposed in order from the object side to the image side.
Also a variable focal length lens system of a positive-negative-negative-positive-positive five-lens-group configuration is known.
The variable focal length lens system of a positive-negative-negative-positive-positive five-lens-group configuration includes a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a negative refracting power, a fourth lens group having a positive refracting power and a fifth lens group having a positive refracting power, disposed in order from the object side to the image side.